Intermittent fasting shows little advantage over conventional diets, review finds
A comprehensive analysis of randomized trials concludes that intermittent fasting is unlikely to produce substantially greater weight loss or improved quality of life for adults who are overweight or living with obesity than conventional dieting advice or no intervention. Review authors say the practice may still affect some metabolic measures, but the evidence is limited and short term.
What the review examined
Researchers pooled results from 22 randomized trials with nearly 2, 000 adult participants to compare short-term intermittent fasting strategies against standard dietary advice or no guidance. The trials ran for up to 12 months and tested a range of approaches, including time-restricted eating—where food intake is confined to a daily window—and regimens that involve very low intake on selected days each week.
The analysis sought to determine whether these limited-eating approaches led to greater weight loss or better reported quality of life than typical calorie-reduction or healthy-eating recommendations. Study sites spanned several regions worldwide, but most trials were small and used varying methods, which investigators say complicates interpretation.
Key findings and study limitations
On average, adults following intermittent fasting lost only modest amounts of weight—about three percent of body weight—over the trial periods. That falls short of the roughly five percent threshold many clinicians regard as clinically meaningful for cardiometabolic benefit. In head-to-head comparisons, intermittent fasting produced weight-loss results similar to traditional dietary counseling; compared with people offered no advice, fasting delivered barely greater weight loss in many trials. Measures of overall quality of life showed little clear improvement.
The authors highlight several important caveats. Many included trials had small sample sizes and limitations in design and reporting, leaving moderate confidence in the central weight-loss finding but lower confidence in other outcomes. Trials used different fasting definitions and protocols, and few assessed longer-term maintenance beyond a year. Investigators also noted scant data on how outcomes vary by sex, baseline body mass index, or cultural context.
Despite the limited impact on weight and quality of life, some mechanistic evidence suggests intermittent fasting could change metabolic processes. Animal studies and preliminary human work indicate potential improvements in insulin sensitivity, reductions in inflammation, and activation of cellular recycling pathways linked to ageing. The review authors call for more robust, longer trials that track clinical endpoints such as diabetes control and cardiovascular risk markers.
Practical takeaways for people considering fasting
The review frames intermittent fasting as one option among several rather than a miracle solution. "Intermittent fasting may be a reasonable option for some people, but the current evidence doesn't justify the enthusiasm we see on social media, " said Luis Garegnani, one of the lead authors. Senior review author Eva Madrid observed that clinicians will need to advise patients on an individual basis, weighing personal preferences, medical history and the likelihood of adherence.
For people thinking about trying intermittent fasting: it may suit those who find time-restricted eating easier to follow than counting calories, but it is not guaranteed to produce superior weight loss. Behavioural factors—such as reduced activity on fasting days or compensatory overeating—can blunt benefits. Anyone with underlying health conditions, particularly diabetes, should discuss changes to eating patterns with a healthcare professional before starting a fasting regimen.
In short, intermittent fasting remains popular and may offer metabolic advantages for some, but current trial evidence does not show substantial weight-loss or quality-of-life gains over conventional dietary approaches. Researchers urge higher-quality, longer-term studies to clarify who might benefit most and whether any metabolic improvements translate into meaningful health outcomes.
